Superabrasive tool and method of manufacturing the same

ABSTRACT

A superabrasive tool such as a superabrasive grindstone ( 101; 102 ), a superabrasive dresser ( 103; 104; 105 ) or a superabrasive lap surface plate ( 106 ) includes a base ( 20 ) of steel and a superabrasive layer ( 10 ) formed on the base ( 20 ). The superabrasive layer ( 10 ) includes superabrasive grains ( 11 ) consisting of diamond grains, cubic boron nitride grains or the like and a holding layer consisting of a nickel plating layer ( 16 ) and a bond layer ( 17 ), or a brazing filler metal layer ( 18 ), holding the superabrasive grains ( 11 ) and fixing the same onto the base ( 20 ). Grooves ( 12 ) or holes ( 14 ) are formed on flat surfaces ( 19 ) of the superabrasive grains ( 11 ) exposed from the holding layer ( 16, 17; 18 ). The holding layer ( 16, 17; 18 ) holding and fixing the superabrasive grains ( 11 ) so that the surfaces of the grains are partially exposed is formed on the base ( 20 ). The grooves ( 12 ) or the holes ( 14 ) are formed by irradiating the surfaces of the superabrasive grains ( 11 ) exposed from the holding layer ( 16, 17; 18 ) with a laser beam ( 50 ). Working of high accuracy can be performed by forming the grooves ( 12 ) or the holes ( 14 ) on the surfaces of the superabrasive grains ( 11 ).

FIELD OF THE INVENTION

The present invention generally relates to a superabrasive tool having asuperabrasive layer holding superabrasive grains by a bond or the likeand a method of manufacturing the same. More specifically, the presentinvention relates to a superabrasive tool such as a superabrasivegrindstone, a superabrasive dresser or a superabrasive lap surface plateand a method of manufacturing the same. A grindstone employingsuperabrasive grains of diamond, cubic boron nitride (CBN) or the likecan be cited as the superabrasive grindstone. As to the superabrasivedresser, a diamond rotary dresser utilized for dressing a conventionalgrindstone of WA or GC (type of JIS) or a vitrified bond CBN grindstonemounted on a grinder or the like in high accuracy can be cited. Adiamond lap surface plate employed for lapping of a silicon wafer,ceramics, optical glass, cemented carbide, cermet or a metal materialcan be cited as the superabrasive lap surface plate.

BACKGROUND INFORMATION

First, a grindstone prepared by bonding superabrasive grains of diamondor CBN with a metal, resin or a vitrified bond is known as asuperabrasive grindstone which is a kind of superabrasive tool. Further,a grindstone prepared by holding and fixing superabrasive grains on abase by electroplating is known as a superabrasive grindstone in theform of holding superabrasive grains in a single layer. Such asuperabrasive grindstone is called an electroplated superabrasivegrindstone. The grains are generally fixed onto the base to such adegree that the superabrasive grains come into contact with each other,and hence the degree of concentration of grains may be too high,depending on the purpose of grinding performed with this grindstone. Asa countermeasure therefor, means are employed for improving the flow ofa grinding fluid and eliminating chips, such as a method of locallyinhibiting electroplating by a method of (1) providing grinding grooveson the grinding surface of the grindstone or (2) locally applying aninsulating paint to the base, and locally forming a part having nosuperabrasive grains on the grinding surface.

On the other hand, the thickness of a plating layer is rendered at least½ the diameter of the superabrasive grains, in order to ensure holdingpower for the superabrasive grains.

With respect to the aforementioned electroplated superabrasivegrindstone, a superabrasive grindstone in which superabrasive grains arefixed onto a base by a brazing filler metal layer is known. As todiamond abrasive grains, for example, the so-called brazing methodutilizing such a characteristic that an alloy consisting of nickel,cobalt and chromium or an alloy consisting of silver, copper andtitanium readily wets surfaces of diamond abrasive grains and directlyfixing diamond abrasive grains onto a base by employing this alloy isalso known.

Further, a porous resin bond grindstone employing fine diamond grains isproposed as a grindstone for attaining working of high accuracy and ahigh grade. Increase of chip pockets or the like is aimed to be achievedby a porous part in this grindstone.

Surface roughness of a ground surface is regarded as being decided bythe effective abrasive grain number per unit surface area of thegrindstone. However, how to grasp the effective abrasive grain numberwith respect to the grain sizes and the degree of concentration of theabrasive grains is not necessarily clear, and there has been thefollowing problem depending on the levels of the grain sizes of theabrasive grains.

In a grindstone employing abrasive grains having relatively large grainsizes, i.e., coarse grains, holding power for the abrasive grains isstrong, fewer abrasive grains are dropped out of the grindstone and theflow of a grinding fluid is also excellent. However, the accuracy of asurface ground by coarse grains is low and its surface roughness islarge. In a grindstone employing abrasive grains having relatively smallgrain sizes, i.e., fine grains, on the other hand, it is possible toincrease the accuracy of a ground surface and to reduce its surfaceroughness. However, holding power for small abrasive grains is weak,more abrasive grains are dropped, and the flow of the grinding fluid isalso inferior. In the grindstone employing fine grains, therefore,grinding performance is low, the abrasive grains become ungrindablefollowing slight wear, and the life of the grindstone is short.

To prepare a diamond rotary dresser, i.e. a kind of superabrasive tool,it is well known to fix diamond abrasive grains to the outer peripheralsurface of a cylindrical base in a single layer, as disclosed inJapanese Patent Laying-Open No. 59-47162, for example.

Another example of a known diamond rotary dresser is disclosed inJapanese Patent Publication No. 1-22115. These diamond rotary dressers,having wide acting ranges, are employed for dressing a conventionalgrindstone of WA or GC (type of JIS) or a CBN grindstone with highaccuracy. Means for densely fixing diamond grains onto a base,flattening surfaces acting on dressing by truing forward end portions ofthe diamond grains and improving dressing accuracy are various meansemployed by the diamond rotary dresser.

However, the formation of flat surfaces on the forward end portions ofthe diamond grains lowers the sharpness of the diamond rotary dresser.Thus, the dressing resistance increases when a conventional grindstoneof WA or GC or a CBN grindstone is dressed. Consequently, there has beensuch a problem that vibration takes place in dressing and the vibrationexerts a bad influence on shaping accuracy of the grindstone, i.e.,transfer accuracy to the grindstone.

Further, a superabrasive lap surface plate is a kind of superabrasivetool. Recently, improvements in the accuracy of flatness and parallelismof a workpiece is required in lapping, due to rapid technologicalinnovation such as high integration in a semiconductor device orsuperprecision in metal working or ceramics working. This results indemands of greater accuracy not only of the lapping machine employed forthis working, but also intensifies the requirement of accuracy andcharacteristics for the lap surface plate.

Lapping refers to a method of working a surface by supplying freeabrasive grains mixed into a lap liquid between a lap surface plate anda workpiece, rubbing the lap surface plate and the workpiece with eachother while applying pressure, scraping the workpiece by rolling actionand scratch action of the free abrasive grains and obtaining a highaccuracy surface.

The lap surface plate employed for conventional lapping is made of castiron. For example, a lap surface plate of spherical graphite cast ironis generally employed for lapping on a silicon wafer. The lap surfaceplate must have such properties that ensure that it is capable ofmaintaining accuracy of a flat surface over a long period, that thematerial is homogeneous without irregularity in hardness, withoutcasting defects that will cause scratching on the surface of theworkpiece, and with a holding ability for abrasive grains. In order tosatisfy the above necessary conditions, cast iron is generally employedas the material for the lap surface plate.

In conventional lapping, however, a great many free abrasive grains areconsumed, and hence, great volumes of mixtures of used free abrasivegrains, chips and a lap liquid, i.e., sludge are generated. As a resultdeterioration of working environment and occurrence of environmentalpollution have become a significant subject of discussion.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide asuperabrasive grindstone capable of improving accuracy of a groundsurface, in which the holding power for superabrasive grains is large,chipping or dropping of superabrasive grains is small and flow of agrinding fluid is also excellent, and a method of manufacturing thesame.

Another object of the present invention is to provide a super-abrasivedresser which can reduce dressing resistance and is thereby capable ofpreventing vibration occurrence in dressing and improving dressingaccuracy, and a method of manufacturing the same.

Further, still another object of the present invention is to provide asuperabrasive lap surface plate which can reduce the generation ofsludge and is capable of performing lapping of high accuracy and highefficiency, and a method of manufacturing the same.

Briefly stated, the object of the present invention is to provide asuperabrasive tool such as a superabrasive grindstone, a superabrasivedresser or a superabrasive lap surface plate capable of improvingworking accuracy and a method of manufacturing the same.

SUMMARY OF THE INVENTION

A superabrasive tool according to the present invention comprises a baseand a superabrasive layer formed on the base. The superabrasive layerincludes superabrasive grains and a holding layer holding and fixing thesuperabrasive grains onto the base. Concave parts are formed on surfacesof the superabrasive grains exposed from the holding layer.

The concave parts include all forms of depressions from thesuperabrasive grain surfaces, such as holes.

According to a preferred embodiment of the superabrasive tool of thepresent invention, concave parts or depressions are formed also on asurface of the holding layer. More preferably, the concave parts formedon the surfaces of the superabrasive grains and the concave parts formedon the surface of the holding layer are continuously formed.

According to another preferred embodiment of the present invention, theconcave parts are formed on the surfaces of the superabrasive grainsprojecting from the holding layer. More preferably, the projectingsurfaces of the superabrasive grains have flat surfaces, and the concaveparts are formed on the flat surfaces.

According to still another embodiment of the superabrasive tool of thepresent invention, the surfaces of the exposed superabrasive grains haveflat surfaces, and the flat surfaces form a substantially parallel planewith the surface of the holding layer. However, the flat surfaces of thesuperabrasive grains preferably project from the surface of the holdinglayer by at least 10 μm. Therefore, it is assumed that the“substantially parallel plane” includes deviation of the surface heightof about 10 μm. Also in case of this embodiment, it is preferable thatconcave parts are formed on the surface of the holding layer. Morepreferably, the concave parts formed on the surfaces of thesuperabrasive grains and the concave parts formed on the surface of theholding layer are continuously formed.

In the superabrasive tool according to the present invention, theholding layer preferably includes a plating layer, or includes a brazingfiller metal layer.

A superabrasive grindstone, a superabrasive dresser, a superabrasive lapsurface plate or the like can be cited as the superabrasive tool towhich the present invention is directed.

The method of manufacturing a superabrasive tool according to thepresent invention comprises a step of forming a holding layer holdingand fixing superabrasive grains on a base so that surfaces thereof arepartially exposed, and a step of forming concave parts by irradiatingwith a laser beam the surfaces of the superabrasive grains exposed fromthe holding layer.

Preferably, the method of manufacturing a superabrasive tool accordingto the present invention further comprises a step of forming concaveparts by irradiating a surface of the holding layer with a laser beam.More preferably, the steps of forming the concave parts on the surfacesof the superabrasive grains and the surface of the holding layer includean operation of continuously forming the concave parts on the surfacesof the superabrasive grains exposed from the holding layer and thesurface of the holding layer by continuously irradiating the same withthe laser beam.

According to another embodiment of the method of manufacturing asuperabrasive tool of the present invention, the step of forming theconcave parts includes an operation of forming the concave parts byirradiating the surfaces of the superabrasive grains projecting from theholding layer with the laser beam.

According to still another embodiment of the method of manufacturing asuperabrasive tool of the present invention, the method furthercomprises a step of substantially uniformly flattening the surfaces ofthe superabrasive grains exposed from the holding layer, and the step offorming the concave parts by irradiating the surfaces with the laserbeam includes an operation of flattening the surfaces of thesuperabrasive grains and thereafter irradiating the surfaces with thelaser beam. In this case, the step of flattening the surfaces of thesuperabrasive grains preferably includes an operation of flattening thesurfaces of the superabrasive grains so that the surfaces of the exposedsuperabrasive grains form a substantially continuous plane that iscoplanar with the surface of the holding layer. More preferably, themethod of manufacturing a superabrasive tool according to the presentinvention further comprises a step of forming concave parts byirradiating the surface of the holding layer with a laser beam, and thesteps of forming the concave parts on the surfaces of the superabrasivegrains and the surface of the holding layer include an operation ofcontinuously forming the concave parts on the flattened surfaces of thesuperabrasive grains and the surface of the holding layer bycontinuously irradiating the same with the laser beam.

Preferably, the step of forming the holding layer in the method ofmanufacturing a superabrasive tool according to the present inventionincludes an operation of forming a plating layer or an operation offorming a brazing filler metal layer.

The step of forming the holding layer including the plating layerpreferably includes the following steps:

(i) a step of sticking the superabrasive grains to a surface of a moldwith a conductive adhesive layer.

(ii) a step of dipping the mold to which the superabrasive grains arestuck in a plating solution of a first metal for forming a plating layerof the first metal partially covering the surfaces of the superabrasivegrains in a thickness less than ½ the mean grain size of thesuperabrasive grains.

(iii) a step of forming a plating layer of a second metal which isdifferent from the first metal on the plating layer of the first metalin a thickness completely covering the superabrasive grains.

(iv) a step of fixing the plating layer of the second metal to the baseby a bond layer.

(v) a step of removing the mold from the superabrasive grains.

(vi) a step of removing the plating layer of the first metal by etchingand partially uniformly exposing the surfaces of the superabrasivegrains.

In the superabrasive tool according to the present invention comprisingthe aforementioned characteristics, the following actions/effects can beattained in response to the types of the tool:

First, in a superabrasive grindstone, sharpness and working accuracybecome excellent, accuracy of a ground surface improves and surfaceroughness of the ground surface can be reduced, while holding power forthe abrasive grains can be improved. At the same time, chipping ordropping of the abrasive grains can be reduced, and flow of a grindingfluid can also be made excellent.

In a superabrasive dresser, dressing resistance can be reduced,sharpness and accuracy improve while occurrence of vibration in dressingcan be prevented, and dressing accuracy can be improved. Particularly inthe superabrasive dresser, a superabrasive dresser improving dressingaccuracy in response to the shape of a grindstone can be structured byforming concave parts only on the surfaces of the superabrasive grainsdressing a shoulder portion or an end portion of the grindstone, or byforming concave parts on the surfaces of the superabrasive grains incorrespondence to only a part to which shaping accuracy is required in aworkpiece.

In a superabrasive lap surface plate, working is performed with fixedabrasive grains in place of conventional working with free abrasivegrains, thereby reducing the generation of sludge. This makes itpossible to maintain a plane of higher accuracy, and lapping of highefficiency can be performed.

Concretely, the first characteristic of the superabrasive grindstoneaccording to the present invention is based on an absolutely new idea,which has both of the respective advantages of a conventional grindstoneemploying fine grains and a grindstone employing coarse grains and iscapable of increasing the effective abrasive grain number withoutincreasing the concentration of the abrasive grains. As a method ofimplementing it, the present invention divides the projecting portionsof the superabrasive grains in an abrasive layer by concave parts orgrooves, and thereby provides a plurality of abrasive grain endsurfaces. According to this method, the effective abrasive grain numbercan be increased analogous to an abrasive surface of fine grains havinga high degree of concentration by: employing coarse grains of largesuperabrasive grains with a relatively low degree of concentration;working the projecting parts from a bond serving as the holding layertherefor into flat surfaces, providing grooves on the flat surfaces,thereby dividing the abrasive surface of the superabrasive grains andforming a plurality of abrasive end surfaces. When the employedsuperabrasive grains are in the form of prisms and flat surfaces existon the projecting parts from the start, or the heights of the projectingparts are extremely uniformly regular, flattening such as truing can beomitted. Further, the grooves are preferably intersectionally providedto be formed just as lines defining clearances on a go board orcheckerboard.

It is also possible to form a sharp insert part by forming grooves onthe projecting surfaces of the superabrasive grains without working theprojecting parts of the superabrasive grains from the bond serving asthe holding layer into flat surfaces. It is not necessary to form thegrooves on the projecting surfaces of all superabrasive grains, andsuperabrasive grains with no grooves may exist. The grooves may beformed on the projecting parts of the superabrasive grains partiallysubjected to flattening such as truing.

When employing superabrasive grains of relatively large grain sizes, itis preferable to employ grains that are substantially regular in size.An excellent effect can be attained by employing superabrasive grainshaving grain sizes of at least 50 μm, more preferably superabrasivegrains having grain sizes within the range of #20 to #40.

When a plating layer is employed as the holding layer holding thesuperabrasive grains, it is possible to omit the operation of workingthe projecting surfaces of the superabrasive grains of a grindstone tobe flat by substantially uniformly regularizing the amounts ofprojection of the superabrasive grains when producing the grindstone.Also, as to the grooves formed on the flattened projecting surfaces ofthe superabrasive grains, the depths and the widths thereof, the angleat which the plurality of grooves intersect in the form of linesdefining clearances on a go board or a checkerboard, and the like can beselected by adjusting the irradiation method of the laser beam. Thus, itis possible to improve the sharpness of the grindstone and eliminationof chips, thereby improving the grinding accuracy.

As to the bond employed as the holding layer holding the superabrasivegrains, resin can also be employed in addition to metal or a vitrifiedbond. The superabrasive layer is formed in a single layer, and hence itis preferable to employ a metal having high bonding strength as thematerial for the bond. The metal is preferably formed by electroplatingor brazing.

In case of flatly working the projecting surfaces of the superabrasivegrains, the superabrasive grains are held on the base with theaforementioned bond, thereafter the flat surfaces are formed whilesubstantially uniformly regularizing the heights of the projecting endsof the superabrasive grains by truing, and the flat surfaces of therespective abrasive grains are irradiated with a laser beam for formingthe grooves.

As hereinabove described, the abrasive surface is formed bysuperabrasive grains whose grain sizes are relatively large. Hence thesurface roughness of a worked surface is essentially relatively large ifground with the grindstone comprising the abrasive surface of suchsuperabrasive grains. In the present invention, however, grooves areformed by irradiating the flat surfaces or the projecting surfaces ofthe superabrasive grains with the laser beam. By substantiallyregularizing the projecting heights of the superabrasive grains and/orforming flat surfaces on the forward end portions of the abrasivegrains, the grooves form a number of abrasive end surfaces on the flatsurfaces or the projecting surfaces. These abrasive end surfaces act asan insert or a flat drag and increase the effective abrasive grainnumber. The accuracy of the worked surface is improved and its surfaceroughness reduced by employing the superabrasive grindstone thusstructured.

Because the grain sizes of the superabrasive grains forming the abrasivesurface are large, a strong abrasive surface can be stably formed byfixing the superabrasive grains to the base by the aforementionedelectroplating, or by fixing the superabrasive grains to the base by anoperation of melting an alloy mainly composed of nickel-cobalt-chromiumor an alloy mainly composed of silver-titanium-copper, i.e., by brazing.Fixing the superabrasive grains to the base by brazing provides greaterholding power for holding the superabrasive grains than fixing thesuperabrasive grains to the base by electroplating, such as nickelplating. Therefore, the amounts of projection of the superabrasivegrains can be increased in case of fixing the superabrasive grains by abrazing method. Consequently, the so-called chip pockets can be enlargedaccording to the brazing method. While it is necessary to hold at least50% of the superabrasive grain when using nickel plating as a holdinglayer for the superabrasive grains, for example, the brazing methodprovides sufficient holding power when merely 20 to 30% of the grain isheld by a brazing filler metal layer.

Further, a space on a surface part of the superabrasive layer formed bythe projecting parts of the large-size superabrasive grains and thesurface of the holding layer is enlarged by the grooves formed on theprojecting parts. The grooves divide the insert and reduce the size ofthe grinding chip. As a result, the flow of the grinding fluid andelimination of the chips even out, and the sharpness improves.

While it has been described that the effective abrasive grain number andthe space on the surface part of the superabrasive layer can beincreased by forming grooves on the surfaces of the superabrasive grainsprojecting from the surface of the holding layer as the above, theeffective abrasive grain number can also be increased in such agrindstone on which the exposed surfaces of the superabrasive grains andthe surface of the holding layer are flattened substantially on the sameplanes, by selecting the depth and the width of the grooves, the angleof intersection in the form of lines defining clearances on a go boardor checkerboard formed by the plurality of grooves and the like byadjusting the irradiation method of the laser beam. In this case, theeffective abrasive grain number can be increased by forming grooves onthe exposed surfaces of the superabrasive grains and the surface of theholding layer when recycling a grindstone, the abrasive surface of whichflattens with use, and the grindstone can be recycled so that prescribedgrinding performance is attained. Further, the grindstone structured asdescribed above can perform dressing when in use or every time the sameis used, as needed.

As hereinabove described, relatively large superabrasive grains ofcoarse grains can be employed in the superabrasive grindstone accordingto the present invention, whereby the absolute value of an embed depthin the holding layer is deeper than a grindstone employing superabrasivegrains of fine grains. Therefore, the degree of bonding by the holdinglayer is strong, and chipping or dropping of the superabrasive grains bygrinding is less.

The grooves are provided on the projecting surfaces or the flattenedexposed surfaces of the superabrasive grains and a number ofsubstantially uniformly regularized abrasive end surfaces are formed, asif superabrasive grains of fine grains were employed. The effectivenumber of abrasive grains increases with respect to the grain sizes, thedegree of concentration of the superabrasive grains. Therefore, it ispossible to improve the sharpness of the grindstone and the accuracy ofthe ground surface. By regularizing the grain sizes of the employedsuperabrasive grains and further regularizing the projecting heights ofthe superabrasive grains from the surface of the holding layer, theeffective abrasive grain number thereby increases. The effectiveabrasive grain number can be increased by irradiating the projectingsurfaces of the superabrasive grains with the laser beam to form groovesin the surfaces. Further, it is possible to provide a superabrasivegrindstone with excellent sharpness and grinding accuracy by irradiatingthe projecting surfaces or the flattened exposed surfaces with the laserbeam to form regular or irregular grooves similar to lines definingclearances on a go board or checkerboard and selecting the number of thegrooves, the intervals between the grooves, the angle at which thegrooves intersect and the like. Therefore, the grindstone of the presentinvention can facilitate a changeover to working with fixed abrasivegrains from working with free abrasive grains, which has generally beendone in high-grade working of electronic, optical components or thelike, for example.

In the superabrasive dresser according to the present invention, groovesare formed on diamond abrasive grains fixed to a diamond rotary dresser,for example. Namely, grooves are formed on the abrasive surface of thediamond grains by irradiating with a laser beam exposed surfaces of thediamond grains projecting from a surface of a holding layer of thediamond rotary dresser or by irradiating exposed surfaces of the diamondgrains substantially on the same plane as the surface of the holdinglayer. This effectively divides the abrasive surfaces of the diamondgrains. Thus, a resistance value in dressing is reduced which preventsthe occurrence of vibration in dressing. Moreover, the dressingoperation can be performed with high efficiency by further improvingdressing accuracy.

The inventors have carried out further repeated trial manufacturing andstudies as to the aforementioned diamond rotary dresser, and havediscovered that it is not necessary to perform the operation of formingthe grooves on the exposed surfaces of the diamond grains and dividingprojecting end surfaces or flattened exposed end surfaces of the diamondgrains over the entire surface where the dresser acts. In dressing agrindstone having a shoulder portion or the like, for example, groovesare formed only on the surface part that effectively dresses theshoulder portion of the grindstone which is a portion that readilycauses burning in an operating surface of the dresser. Or, as todressing a portion of the grindstone to which accuracy is particularlyrequired, the truing amount of the diamond layer is large and sharpnessdecreases due to the fact that the flat part areas of the diamond grainsincrease, and hence grooves are formed only on this portion. It is mosteffective in manufacturing and use of the dresser to form the grooves ononly such a necessary portion.

Also in the dresser according to the present invention, relatively largesuperabrasive grains of coarse grains can be employed similarly to thegrindstone, whereby bonding strength by the holding layer is strong, andchipping and dropping of the superabrasive grains by grinding are less.Also in the dresser of the present invention, the effective abrasivegrain number is increased with respect to the grain sizes, the degree ofconcentration of the employed abrasive grains. A dresser that furtherimproves sharpness and accuracy can be provided by selecting the numberof the grooves, the intervals between the grooves, the angle at whichthe grooves intersect and the like. No end surface burning is caused indressing and the resistance value in dressing and occurrence ofvibration can also be reduced by forming the grooves only on the partfor dressing the shoulder portion of the grindstone or a part to whichaccuracy is required in particular.

The superabrasive lap surface plate according to the present inventionsolves the conventional problems by changing from working with freeabrasive grains to working with fixed abrasive grains. This reduces thegeneration of sludge greatly and enables operation in a cleanenvironment. It is also possible to continue to maintain a high-accuracyplane of the lap surface plate over a long period. Efficiency in alapping operation is also improved by working with fixed abrasivegrains. To this end, grooves are formed on diamond grains fixed to adiamond lap surface plate of the present invention. Namely, the groovesare formed by irradiating with a laser beam exposed surfaces of diamondgrains fixed to project from a surface of a bond layer that is a holdinglayer of the diamond lap surface plate, or by irradiating surfaces ofdiamond grains fixed to be exposed substantially on the same plane asthe surface plane of the holding layer, for dividing abrasive surfacesof the diamond grains.

In the superabrasive tool according to the present invention, further,at least one or two holes are formed by irradiating the exposed surfacesof the superabrasive grains with a laser beam, in place of forming thegrooves by irradiating the exposed surfaces of the superabrasive grainswith the laser beam and dividing the abrasive surfaces of thesuperabrasive grains. It is preferable that the diameter and the depthof this hole are at least 20 μm, and more preferably the diameter of thehole is at least 50 μm and the depth of the hole is at least 30 μm.Further, it is more preferable that the holes are formed on an exposedsurface of the holding layer holding the superabrasive grains and theboundary between the exposed surfaces of the superabrasive grains andthe exposed surface of the holding layer.

In the aforementioned structure, the effective abrasive grain number canbe increased analogous to an abrasive surface employing superabrasivegrains of fine grains in a high degree of concentration, by employingsuperabrasive grains of coarse grains whose degree of concentration isrelatively low. This is accomplished by working the exposed surfaces orthe surfaces projecting from the holding layer into flat surfaces andforming at least one or two holes on the flat surfaces so thatperipheral edge portions of the holes act as an insert. When theemployed superabrasive grains are in the form of prisms and theprojecting surfaces are flat surfaces from the start, or when theheights of the exposed surfaces of the superabrasive grains areextremely uniformly regular, a flattening step such as truing may beomitted. The holes may be formed on the exposed surfaces withoutflattening the exposed surfaces of the superabrasive grains, as a matterof course.

It is necessary that the diameter of the holes formed on the exposedsurfaces of the superabrasive grains is at least 50 μm and the depth isat least 30 μm, in order to make the peripheral edge portions of theholes act as an insert, and in consideration of elimination of chips. Asto the relatively large superabrasive grains, it is preferable to employthose grain sizes that are substantially uniformly regular. Further, thegrain sizes of the superabrasive grains are preferably at least 50 μm,and an excellent action/effect can be attained when selecting the grainsizes within the range of #20 to #40.

Further, a superabrasive tool which provides excellent sharpness andsuperior elimination of chips is achieved, due to the fact that theholes are formed not only on the exposed parts of the superabrasivegrains but also on the exposed part of the holding layer and on theboundary between the exposed parts of the superabrasive grains and theexposed part of the holding layer. It is effective that the holes areformed on the overall exposed part of the superabrasive layer includingthe holding layer, and that the open areas of the holes preferablyconstitute at least 20% with respect to the overall surface area of theexposed part of the superabrasive layer.

According to the superabrasive tool with holes formed on the exposedsurfaces of the superabrasive grains, the peripheral edge portions ofthe holes act as an insert or a flat drag, and an effect similar to thatof increasing the effective abrasive grain number is attained.Therefore, accuracy of the worked surface is improved. Further, theholes are isolated from each other and it is estimated that there is nodanger of the tool breaking during grinding because of a pressing forcedue to the presence of these holes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a cup-type grindstone to which thepresent invention is applied.

FIG. 2 is a sectional view showing the cup-type grindstone to which thepresent invention is applied.

FIG. 3 is a perspective view showing a straight-type grindstone to whichthe present invention is applied.

FIG. 4 is a sectional view showing the straight-type grindstone to whichthe present invention is applied.

FIG. 5 is a perspective view showing a rotary dresser to which thepresent invention is applied.

FIG. 6 is a sectional view showing the rotary dresser to which thepresent invention is applied.

FIG. 7 is a sectional view showing a rotary dresser comprising ashoulder portion to which the present invention is applied.

FIG. 8 is a sectional view showing a rotary dresser comprising an endsurface to which the present invention is applied.

FIG. 9 is a perspective view showing a lap surface plate to which thepresent invention is applied.

FIG. 10 is a sectional showing the lap surface plate to which thepresent invention is applied.

FIG. 11 is a model diagram showing laser beam machining in case ofirradiating an abrasive surface of the cup-type grindstone to which thepresent invention is applied with a laser beam in a normal direction.

FIG. 12 is a model diagram showing laser beam machining in case ofirradiating an operating surface or an abrasive surface of thestraight-type grindstone or the rotary dresser to which the presentinvention is applied with a laser beam in a normal direction.

FIG. 13 is a model diagram showing laser beam machining in case ofirradiating the abrasive surface of the straight-type grindstone or therotary dresser to which the present invention is applied with laserbeams in a tangential direction and a normal direction.

FIG. 14 is a model diagram showing laser beam machining in case ofirradiating an abrasive surface of the lap surface plate to which thepresent invention is applied with a laser beam in a normal direction.

FIG. 15 to FIG. 22 are partial sectional views showing various ofgrooves or holes formed on exposed parts of superabrasive grains thatproject from holding layers in accordance with the present invention.

FIG. 23 to FIG. 30 are partial sectional views showing various forms ofgrooves or holes formed on flat surfaces of exposed surfaces ofsuperabrasive grains that project from holding layers and are flattenedin accordance with the present invention.

FIG. 31 to FIG. 38 are partial sectional views showing various forms ofgrooves or holes formed on exposed surfaces of superabrasive grainsand/or exposed surfaces of holding layers in accordance with the presentinvention when the exposed surfaces of the superabrasive grains and theholding layer are on the same plane.

FIG. 39 to FIG. 41 are partial plan views showing arrangements ofgrooves formed on exposed surfaces of superabrasive grains and/orexposed surfaces of holding layers in accordance with the presentinvention;

FIG. 42 is an enlarged partial sectional view showing a projecting endsurface of a superabrasive grain in a superabrasive grindstone ofExample 1;

FIG. 43 is a microphotograph showing a state of an abrasive surfaceafter truing the abrasive surface in the superabrasive grindstone ofExample 1 and before irradiating the same with a laser beam;

FIG. 44 is a microphotograph showing a state of the abrasive surfaceafter being irradiated with a laser beam in the superabrasive grindstoneof Example 1;

FIG. 45 is a diagram showing a longitudinal sectional side surfacebefore performing truing in a superabrasive grindstone of Example 2;

FIG. 46 is a sectional view showing a superabrasive layer employed forillustrating a manufacturing step for the superabrasive grindstone ofExample 2;

FIG. 47 is a sectional view showing the superabrasive layer employed forillustrating a manufacturing step after FIG. 46 in the superabrasivegrind-stone of Example 2;

FIG. 48 is a diagram showing the relations between the grain sizes ofsuperabrasive grains and the number of effective abrasive grains inconventional superabrasive grindstones and superabrasive grindstonesaccording to the present invention;

FIG. 49 is a partial sectional view showing a part of a superabrasivelayer in a superabrasive grindstone of Example 3;

FIG. 50 is a microphotograph showing a state of an abrasive surface ofthe superabrasive grindstone of Example 3;

FIG. 51 is a diagram showing a mode of performing dressing with adiamond rotary dresser in Example 6;

FIG. 52 is a diagram showing a mode of performing dressing with adiamond rotary dresser in Example 7;

FIG. 53 is a partial sectional view showing a section of a diamond layerin a diamond lap surface plate of Examples 9 and 10;

FIG. 54 is a diagram showing comparison of working speeds of lappingbetween Examples 9 and 10 and a conventional one;

FIG. 55 is a partial sectional view showing a section of a superabrasivelayer of a superabrasive tool formed with holes; and

FIG. 56 is a microphotograph showing a surface of the superabrasivelayer of the superabrasive tool formed with the holes.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

First, the types of superabrasive tools to which the present inventionis applied are described.

As shown in FIG. 1, a superabrasive layer 10 is formed on one endsurface of a base 20 having a cylindrical shape in a cup-typesuperabrasive grindstone 101. The cup-type superabrasive grindstone 101has a mounting shaft hole 30. A surface of the rotating superabrasivelayer 10 of the cup-type superabrasive grindstone 101 comes into contactwith a workpiece and grinding is performed by rotation about thismounting shaft hole 30. As shown in FIG. 2, the cup-type superabrasivegrindstone 101 has a diameter D, and has a width W₁ of the abrasivesurface.

As shown in FIG. 3, a superabrasive layer 10 is formed on an outerperipheral surface of a cylindrical base 20 in a straight-typesuperabrasive grindstone 102. An abrasive surface of the rotatingsuperabrasive layer 10 comes into contact with a workpiece by rotatingthe straight-type superabrasive grindstone 102 about a mounting shafthole 30 whereby grinding is performed. As shown in FIG. 4, thestraight-type superabrasive grindstone 102 has a diameter D and athickness T.

As shown in FIG. 5, a superabrasive layer 10 is formed on an outerperipheral surface of a base 20 in a superabrasive dresser, e.g., adiamond rotary dresser 103. A surface of the superabrasive layer 10comes into contact with a surface of a grindstone by rotating thesuperabrasive dresser 103 about a mounting shaft hole 30 wherebydressing of the grindstone is performed. As shown in FIG. 6, thesuperabrasive dresser 103 has a diameter D and a thickness T.

As shown in FIG. 7, a superabrasive layer 10 is formed on an outerperipheral surface of a base 20 in a superabrasive dresser 104. The base20 has a shoulder portion 21, and the superabrasive layer 10 is formedalso on this shoulder portion 21. As described later, grooves arepreferably formed only on the superabrasive layer 10 positioned on theshoulder portion 21 in accordance with the present invention.

As shown in FIG. 8, further, a superabrasive layer 10 is formed on anouter peripheral surface of a base 20 in a superabrasive dresser 105.The base 20 has end surfaces 22 and 23 which are opposed to each other.The superabrasive layer 10 is formed also on these end surfaces 22 and23. Grooves according to the present invention are preferably formedonly on the superabrasive layer positioned on the end surfaces 22 and23.

Also in the superabrasive dressers 104 and 105 shown in FIG. 7 and FIG.8, surfaces of the rotating superabrasive layers 10 come into contactwith abrasive surfaces of grindstones by rotation about mounting shaftholes 30 so that dressing of the grindstones is performed.

As shown in FIG. 9, a superabrasive layer 10 is fixed onto one endsurface of a base 20 in a superabrasive lap surface plate according tothe present invention, e.g., a diamond lap surface plate 106. Lapping isperformed by rubbing a workpiece against a surface of the rotatingsuperabrasive layer 10 while applying pressure by rotating thesuperabrasive lap surface plate 106 about a mounting shaft hole 30. Thesuperabrasive lap surface plate 106 has a diameter D and a thickness Tas shown in FIG. 10.

In every aforementioned superabrasive tool, abrasive grains of diamond,cubic boron nitride (CBN) or the like are employed as superabrasivegrains forming the superabrasive layer 10. A material made of a metal isemployed as the base 20, and cast iron or the like is employed for thebase 20 of the superabrasive lap surface plate 106 in particular.

Methods of forming concave parts or concavities such as grooves or holeson surfaces of the superabrasive layers of the aforementioned varioustypes of superabrasive tools are now described.

As shown in FIG. 11, concavities such as grooves or holes are formed ona surface of the superabrasive layer 10, i.e., exposed surface(s) of thesuperabrasive grains or a holding layer, by irradiating the surface ofthe superabrasive layer of the cup-type superabrasive grindstone 101with a laser beam 50 from a laser beam machining unit 40 in a normaldirection. When forming grooves or holes on a surface of thesuperabrasive layer 10 of the straight-type superabrasive grindstone 102or the superabrasive dresser 103, 104 or 105, the surface of thesuperabrasive layer 10 is irradiated with a laser beam 50 from a laserbeam machining unit 40 from the normal direction, as shown in FIG. 12 or13. When forming the grooves, the superabrasive layer 10 of thestraight-type superabrasive grindstone 102 or the superabrasive dresser103, 104 or 105 may be irradiated with the laser beam 50 from atangential direction, as shown in FIG. 13. When forming grooves or holeson the surface of the superabrasive layer 10 of the superabrasive lapsurface plate 106, the surface of the superabrasive layer 10 isirradiated with a laser beam 50 from a normal direction.

Various forms of the grooves or holes formed by irradiating the surfaceof the superabrasive layer 10 with the laser beam as described above aredescribed.

Forms of grooves or holes in such cases when exposed parts ofsuperabrasive grains 11 project as shown in FIG. 15 to FIG. 22 will nowbe described. In FIG. 15, FIG. 17, FIG. 19 and FIG. 21, thesuperabrasive layers 10 comprise superabrasive grains 11, nickel platinglayers 16 holding the superabrasive grains 11, and bond layers 17bonding the nickel plating layers 16 to the bases 20. As shown in FIG.16, FIG. 18, FIG. 20 and FIG. 22, on the other hand, the superabrasivegrains 11 are held by brazing filler metal layers 18, and directly fixedto the bases 20.

As shown in FIG. 15 and FIG. 16, the exposed parts of the superabrasivegrains 11 are not flattened, but in irregular states. Plural grooves 12are formed on the exposed surfaces of the superabrasive grains 11. Asshown in FIG. 17 and FIG. 18, grooves 12 are formed on surfaces ofunflattened superabrasive grains 11, and grooves 13 are formed on asurface of the nickel plating layer 16 or the brazing filler metal layer18 serving as the holding layer. In embodiments shown in FIG. 19 andFIG. 20, holes 14 are formed on unflattened exposed surfaces of thesuperabrasive grains 11. In embodiments shown in FIG. 21 and FIG. 22,holes 14 are formed on exposed surfaces of unflattened superabrasivegrains 11, and holes 15 are formed on the surface of the nickel platinglayer 16 or the brazing filler metal layer 18 serving as the holdinglayer.

Various forms of grooves or holes in such cases when exposed parts ofsuperabrasive grains 11 comprise flat surfaces 19 as shown in FIG. 23 toFIG. 30 will now be described. In embodiments of FIG. 23, FIG. 25, FIG.27 and FIG. 29, the superabrasive layers 10 comprise the superabrasivegrains 11, nickel plating layers 16 holding the superabrasive grains 11,and bond layers 17 for bonding the nickel plating layers 16 to the bases20. In embodiments shown in FIG. 24, FIG. 26, FIG. 28 and FIG. 30, onthe other hand, the superabrasive layers 10 comprise the superabrasivegrains 11 and brazing filler metal layers 18 holding the superabrasivegrains 11 and directly fixing the same to the bases 20.

As shown in FIG. 23 and FIG. 24, grooves 12 are formed only on the flatsurfaces 19 of the superabrasive grains 11. As shown in FIG. 25 and FIG.26, not only grooves 12 are formed on the flat surfaces 19 of thesuperabrasive grains 11, but also grooves 13 are formed on a surface ofthe nickel plating layer 16 or the brazing filler metal layer 18 servingas the holding layer. As shown in FIG. 27 and FIG. 28, holes 14 areformed on the flat surfaces 19 of the superabrasive grains 11. As shownin FIG. 29 and FIG. 30, not only holes 14 are formed on the flatsurfaces 19 of the superabrasive grains 11, but also holes 15 are formedon a surface of the nickel plating layer 16 or the brazing filler metallayer 18 serving as the holding layer.

Various forms of grooves or holes in such cases when exposed surfaces ofsuperabrasive grains 11 are on the same plane as surfaces of nickelplating layers 16 or brazing filler metal layers 18 as shown in FIG. 31to FIG. 38 are described. In embodiments shown in FIG. 31, FIG. 33, FIG.35 and FIG. 37, the superabrasive layers 10 comprise the superabrasivegrains 11, the nickel plating layers 16 holding the superabrasive grains11, and bond layers 17 fixing the nickel plating layers 16 to the bases20. In embodiments shown in FIG. 32, FIG. 34, FIG. 36 and FIG. 38, onthe other hand, the superabrasive layers 10 comprise the superabrasivegrains 11, and the brazing filler metal layers 18 holding and fixing thesuperabrasive grains 11 to the bases 20.

As shown in FIG. 31 and FIG. 32, grooves 12 are formed on flat surfaces19 of the superabrasive grains 11. As shown in FIG. 33 and FIG. 34,grooves 12 are formed on flat surfaces 19 of the superabrasive grains11, and grooves 13 are formed on a surface of the nickel plating layer16 or the brazing filler metal layer 18 serving as the holding layer. Asshown in FIG. 35 and FIG. 36, holes 14 are formed on flat surfaces 19 ofthe superabrasive grains 11. As shown in FIG. 37 and FIG. 38, holes 14are formed on flat surfaces 19 of the superabrasive grains 11, and holes15 are formed on a surface of the nickel plating layer 16 or the brazingfiller metal layer 18 serving as the holding layer.

Embodiments of the arrangement of grooves formed on superabrasive layersof superabrasive tools will now be described. In the embodiment shown inFIG. 39, grooves 12 are formed only on exposed surfaces of superabrasivegrains 11. The large number of grooves 12 are formed to be orthogonal toeach other, and arranged in the form of lines defining clearances on ago board or a checkerboard. The distances between the large number ofgrooves 12 extending in the transverse direction in parallel with eachother and the large number of grooves 12 extending in the verticaldirection in parallel with each other, i.e., a groove-to-groove pitch Pis set at a prescribed value so that the grooves in the form of linesdefining clearances on a go board or checkerboard are formed byirradiating the same with a laser beam.

In the embodiment shown in FIG. 40, a large number of grooves 12extending in the vertical direction and in the transverse direction inthe form of lines defining clearances on a go board or checkerboard areformed to extend not only on exposed surfaces of superabrasive grains 11but on a surface of a nickel plating layer 16 or a brazing filler metallayer 18 serving as the holding layer.

As shown in FIG. 41, further, a large number of grooves 12 extending inoblique directions to intersect with each other may be formed to extendon exposed surfaces of superabrasive grains 11 and a surface of a nickelplating layer 16 or a brazing filler metal layer 18 serving as theholding layer. In this case, too, the distances between the grooves 12extending in parallel with each other, i.e., a groove-to-groove pitch Pis set at a prescribed value and grooves in the form of lines definingclearances on a go board or checkerboard are formed by applying a laserbeam while relatively moving the same by a prescribed interval at atime.

EXAMPLE 1

The cup-type superabrasive grindstone 101 shown in FIG. 1 and FIG. 2 wasprepared. The diameter D of the grindstone was 125 mm, and the width W₁of the abrasive surface was 7 mm. Diamond grains of #18/20 in grain size(800 to 1000 μm in grain size) were employed as the superabrasivegrains. The superabrasive layer 10 was formed by holding and fixing thediamond grains on the base of the grindstone by nickel plating.Thereafter the surface of each superabrasive grain 11 projecting fromthe nickel plating layer 16 was trued (a thickness of about 30 μm wasremoved from the grain 11) with a diamond grindstone of #120 in grainsize for forming the flat surface 19, as shown in FIG. 23. Amicrophotograph (magnification: 40) showing a state after truing theabrasive surface is shown in FIG. 43.

Thereafter the surface of the superabrasive layer 10 was irradiated withthe laser beam 50 from the laser beam machining unit 40 in the normaldirection as shown in FIG. 11. As to the laser beam irradiationconditions to this abrasive surface, the input value was set at 5 kHzand the output was set at 2.5 W with a YAG laser. The grooves 12 wereformed on the flat surface 19 of the superabrasive grain 11 by thislaser beam irradiation, as shown in FIG. 23. Further, grooves at thegroove-to-groove pitch P of 50 μm including 16 to 20 grooves extendingin the same direction in parallel with each other were formed by settingthe irradiation pitch of the laser beam at 50 μm and setting the pitchnumber at 16 to 20, as shown in FIG. 39. The formation of the grooves bylaser beam irradiation was performed by rotating the cup-typesuperabrasive grindstone 101 shown in FIG. 1 about the mounting shafthole 30 at a peripheral speed of 250 to 500 mm/min.

Sections of the grooves 12 formed on the flat surface 19 of thesuperabrasive grain 11 in the aforementioned manner are shown in FIG.42. The groove-to-groove pitch P was 50 μm, the width W of the grooveswas 30 μm, the length W₀ of the flat parts between the grooves was 20μm, the length L of the flat surface was 800 to 1000 μm, and the depth Hof the grooves was 14 to 18 μm.

In correspondence to FIG. 39, a microphotograph (magnification: 40)showing the arrangement of the grooves formed by irradiating theabrasive surface after truing with the laser beam is shown in FIG. 44.Referring to FIG. 44, those areas appearing black are flat surfaces ofdiamond grains. Where regular grooves have been formed by laser beamirradiation, flat areas of 20 μm square serve as cutting edges as can beseen in the form of clear lines defining clearances on a go board orcheckerboard. Crushed material can be partially seen.

These parts in the form of lines defining clearances on a go board orcheckerboard form an insert or a flat drag, and grinding progresseswhile causing fine chips similarly to a grindstone employing finegrains. The chips and the grinding fluid smoothly flow through the spacebetween the projecting portion of the superabrasive grain 11 and thenickel plating layer 16 and the spaces of the grooves 12 formed on theflat surface 19 of the superabrasive grain 11 in the section shown inFIG. 23. Moreover, the superabrasive grain 11 is a coarse grain which isdeeply and tightly held by the nickel plating layer 16, whereby nohindrance results from the grains dropping out of the holding layer.

The depth and the width of the grooves, the number, presence/absence ofintersection of the grooves, whether or not the intersection anglesbetween the grooves are equalized with each other on the right and leftsides and the like can be freely selected in response to the workpiece,grinding conditions and the like.

As hereinabove described, the superabrasive grindstone of the presentinvention brings the structure of the abrasive surface into a specificstructure, and hence it is necessary to bring the superabrasive grainsinto one layer.

When the projecting end surfaces of the superabrasive grains are notflat surfaces, the laser beam is applied after forming flat surfaces byperforming truing. Therefore, the grain sizes of the superabrasivegrains may not necessarily be substantially uniformly regular, and theamounts of projection thereof may not be regular.

If the grain sizes of the superabrasive grains are not substantiallyuniformly regular, however, prescribed function/effect cannot besufficiently attained due to the fact that the number of superabrasivegrains on which grooves cannot be formed on the flat surfaces of thesuperabrasive grains increases. When the amounts of projection of thesuperabrasive grains are substantially uniformly regular, it is easy toperform truing, and there is such an effect that prescribed grooves canbe formed even if the amount of removal by truing is small, or withoutperforming truing as the case may be. As the inventors have proposed inJapanese Patent Laying-Open No. 8-229828, therefore, it is preferable tomanufacture a grindstone with regularized amounts of projection ofsuperabrasive grains and to perform grooving by irradiating its abrasivesurface with a laser beam.

EXAMPLE 2

FIG. 45 is a diagram showing a longitudinal sectional side surface of astraight-type superabrasive grindstone 102 before performing truing.FIG. 46 and FIG. 47 are sectional views showing a superabrasive layeremployed for illustrating manufacturing steps for substantiallyregularizing the amounts of projection of superabrasive grains. Amanufacturing method for regularizing the amounts of projection of thesuperabrasive grains will now be described with reference to thesedrawings.

As shown in FIG. 46, superabrasive grains 11 consisting of diamondgrains of #30/40 in grain size are spread and held in one layer on asurface of a mold 60 of carbon with a conductive adhesive layer 70 suchas synthetic resin containing powder of copper. A copper plating layer80 of 60 to 100 μm in thickness was formed by dipping this mold 60 in aplating solution of copper as such or after hardening the resin byheating. Then, the plating solution was exchanged and a nickel platinglayer 16 of 1.5 mm in thickness completely covering the superabrasivegrains 11 was formed on the copper plating layer 80.

Respective conditions of the copper plating and the nickel plating wereas follows:

Copper Plating

Composition of Solution

copper pyrophosphate: 75 to 105 g/l

metal copper: 26 to 36 g/l

potassium pyrophosphate: 280 to 370 g/l

aqueous ammonia: 2 to 5 cc/l

brightener: 1 to 4 cc/l

Plating Conditions

current density: 0.2 A/dm²

temperature: 45 to 50° C.

Nickel Plating

Composition of Solution

nickel sulfate: 250 g/l

nickel chloride: 45 g/l

boric acid: 40 g/l

brightener: 1 g/l

Plating Conditions

current density: 1 A/dm²

temperature: 45 to 50° C.

Then, the nickel plating layer 16 was integrally bonded to the outeredge of a base 20 of steel with a bond layer 17 consisting of a lowmelting point alloy, and thereafter the mold 60 was broken and removed,as shown in FIG. 47. The thickness of the bond layer 17, which was setat 2 mm, can be increased/reduced as needed. Further, the mold 60 may beremoved before bonding of the nickel plating layer 16 and the base 20.

Thereafter the overall base 20, or only the plated part was dipped in anetching solution of copper for dissolving/removing the copper platinglayer 80. In this case, the etching, which was performed by electrolyticetching, can also be performed by chemical etching. At this time, thenickel plating layer 16 is not dissolved, holding of the superabrasivegrains 11 by the nickel plating layer 16 is strong, and only apreviously set thickness part of the copper plating layer 80 iscompletely dissolved/removed, whereby substantially uniform amounts ofprojection of the superabrasive grains 11 are ensured. If any remainderof the resin of the conductive adhesive is recognized on the surface ofthe copper plating layer 80, this resin may be removed by heatingdecomposition or machining. While the method of sticking thesuperabrasive grains 11 to the mold 60 with the conductive adhesive hasbeen described in the aforementioned Example, superabrasive grains suchas diamond grains may be floated in the plating solution for bonding thesuperabrasive grains to the surface of the mold with formation of theplating layer.

The longitudinal sectional side surface of the straight-typesuperabrasive grindstone 102 formed in the aforementioned manner isshown in FIG. 45. As shown in FIG. 45, the superabrasive grains 11consisting of diamond grains of #30/40 in grain size (602 μm in meangrain size) substantially uniformly projected from the surface of thenickel plating layer 16 of about 1.5 mm in thickness with projectionheights of 60 to 100 μm. The bond layer 17 integrally bonding the nickelplating layer 16 and the outer edge of the base 20 of steel was a layerof about 2 mm in thickness consisting of a low melting point alloy.Further, the nickel plating layer 16 sufficiently tightly fixed thesuperabrasive grains 11 with no loosening of a portion around thesuperabrasive grains 11. The diameter D of the straight-typesuperabrasive grindstone 102 was 70 mm, the hole diameter D₀ of themounting shaft hole 30 was 35 mm, and the thickness T was 22 mm.

A flat surface was formed on an abrasive surface of the straight-typesuperabrasive grindstone manufactured in the aforementioned mannerdirectly or by truing similarly to Example 1, and thereafter a laserbeam was applied for forming grooves on the projecting surfaces of thesuperabrasive grains. In this case, the irradiation direction of thelaser beam 50 may be either in the normal direction or in the tangentialdirection with respect to the superabrasive layer, as shown in FIG. 13.

The shape accuracy, the roundness and the surface roughness of a fixingsurface of the mold 60 on which the superabrasive grains 11 are fixed bythe copper plating layer 80 are reflected in the uniformity of theprojecting heights of the superabrasive grains 11 as such. Therefore, itis important to pay attention to various parameters of the mold 60, suchas the selection of material for the mold, working of the mold, surfacefinishing of the mold, and the like. Incidentally, the projectingheights of the superabrasive grains 11 were substantially uniform whenemploying a mold prepared by finishing the shape accuracy and theroundness within 1.5 μm and the surface roughness within 1.5 μm Rmax bygrinding the fixing surface of the mold 60.

FIG. 48 is a graph by a logarithmic scale showing the relations betweenthe grain sizes (μm) of the superabrasive grains and the numbers of theeffective abrasive grains (/cm²) of conventional superabrasivegrindstones and of superabrasive grindstones manufactured in accordancewith Example 2, respectively. Referring to FIG. 48, black squaresindicate measurement results showing the relations between the grainsizes of the superabrasive grains and the numbers of the effectiveabrasive grains before forming the grooves in accordance with Example 2.Namely, the data for the black squares were measured in relation tosuperabrasive grindstones that were substantially uniformly regularizedwith respect to the amounts of projection of the superabrasive grainsand uniformalized with respect to the heights of the projecting endsurfaces. With respect to this, it is understood that the projecting endsurfaces are divided and the numbers of the effective abrasive grainsincrease, as shown by the large black circles when the amounts ofprojection of the superabrasive grains are regularized, the heights ofthe projecting end surfaces are uniformalized, and grooves arethereafter formed by irradiation with laser beams, in accordance withthe present invention. Small black circles reflect measurements inrelation to the conventional superabrasive grindstones (conventionalwheels). “After truing” shows the results measured in relation tosuperabrasive grindstones before forming the grooves in Example 2, and“laser beam machining” shows the results measured in relation tosuperabrasive grindstones after forming grooves in accordance withExample 2.

Thus, it is possible to implement an effective abrasive grain numberequivalent to fine grains or exceeding the same in the superabrasivegrindstone of the present invention employing coarse grains assuperabrasive grains. This means that an abrasive space including chippockets of each superabrasive grain is increased, and contributes to theeffect of improving the sharpness of the grindstone and the grindingaccuracy.

EXAMPLE 3

The cup-type superabrasive grindstone 101 shown in FIG. 1 and FIG. 2 wasprepared. The diameter D of the cup-type superabrasive grindstone 101was 125 mm, and the width W₁ of the abrasive surface was 7 mm. Diamondgrains of #18/20 in grain size (800 to 1000 μm in grain size) wereemployed as the superabrasive grains. These diamond grains were fixed tothe base of the grindstone by a nickel plating layer as the holdinglayer.

Flat surfaces were formed by truing exposed surfaces of the diamondgrains with a diamond grindstone of #120 in grain size so thatprojecting surfaces of the fixed diamond grains were on the same planeas the surface of the nickel plating layer. Thereafter continuousgrooves were formed on the flat surfaces of the diamond grains servingas the superabrasive grains and the surface of the nickel plating layerserving as the holding layer by irradiating the flat surfaces with thelaser beam 50 from the normal direction as shown in FIG. 11 whilerotating the grindstone at a peripheral speed of 250 to 500 mm/min. AYAG laser was employed for the laser beam. As to irradiation conditionsof the laser beam, the input value was set at 5 kHz and the output wasset at 2.5 W. Thus, grooves 12 were formed on the flat surface 19 of thesuperabrasive grain 11, and grooves 13 were formed on the surface of thenickel plating layer 16 too, as shown in FIG. 33.

Further, grooves in the form of lines defining clearances on a go boardor checkerboard at a groove-to-groove pitch P of 50 μm including 16 to20 grooves extending in the same direction in parallel with each otherwere formed by performing irradiation. The irradiation pitch of thelaser beam was set at 50 μm and the pitch number at 16 to 20, as shownin FIG. 40.

As shown in FIG. 49, the grooves 12 were formed on the flat surface 19of each superabrasive grain 11, and the grooves 13 were formed on thesurface of the nickel plating layer 16. The length L of the flat surfaceof the superabrasive grain 11 was 800 to 1000 μm, the width W of thegrooves was 30 μm, the depth H of the grooves was 14 to 18 μm, and thelength W₀ of the flat parts between the grooves was 20 μm. FIG. 50 is amicrophotograph (magnification: 160) showing the arrangement of groovesformed after truing by irradiating the trued abrasive surface with alaser beam in correspondence to FIG. 40. Those areas appearing gray inFIG. 50 are the flat surfaces of the diamond grains. It is observed thatregular grooves are continuously formed by the laser beam on the surfaceof the nickel plating layer which appears white.

Edges of these grooves act as an insert or a flat drag, and grindingprogresses while causing small chips similarly to a grindstone employingdiamond grains of fine grains. Moreover, because the diamond grains arecoarse grains, they are deeply and strongly held by the nickel platinglayer as the holding layer, and consequently, cause no hindrance bydropping from the holding layer.

The depth and the width of the grooves, the number of the grooves,presence/absence of intersection between the grooves, whether or not theintersection angles between the grooves are equalized with each other onthe right and left sides and the like can be freely selected in responseto the workpiece, grinding conditions and the like.

As hereinabove described, the superabrasive grindstone of the presentinvention brings the structure of the abrasive surface into a specificstructure, and hence it is necessary to bring the superabrasive grainsinto one layer. When the surface of the superabrasive layer is not aflat surface, the laser beam is applied after forming a flat surface bytruing similarly to the aforementioned Example, and hence the grainsizes of the superabrasive grains may not necessarily be regular.

If the grain sizes are not substantially uniformly regular, however, thenumber of superabrasive grains on which grooves cannot be formed on flatsurfaces increases and the prescribed function/effect cannot besufficiently attained. If the grain sizes of the superabrasive grainsare substantially uniformly regular, it is easy to perform truing, andthere is such an effect that prescribed grooves can be formed even ifthe amount of removal by truing is small, or without performing truingas the case may be.

EXAMPLE 4

A diamond rotary dresser was prepared as the straight-type superabrasivedresser 103 shown in FIG. 5 and FIG. 6. The diameter D of the diamondrotary dresser was 80 mm, and the thickness T was 25 mm.

Grooves were formed on the superabrasive layer 10 as shown in FIG. 33.Diamond grains of #50/60 in grain size (grain size: 260 to 320 μm) wereemployed as the superabrasive grains 11. The superabrasive grains 11were held by a nickel plating layer 16 serving as the holding layer, andbonded to the base 20 of steel through the bond layer 17 consisting of alow melting point alloy. The grooves 12 were formed on the flat surface19 of each superabrasive grain 11, and grooves 13 were formed on thesurface of the nickel plating layer 16.

Formation of the grooves 12 and 13 was performed as follows: Projectingexposed surfaces of the superabrasive grains 11 were trued with adiamond grindstone by a thickness of 3 μm, and so worked that the flatsurfaces 19 of the superabrasive grains 11 and the surface of the nickelplating layer 16 were flush with each other. Thereafter the grooves wereformed by irradiating the surface of the superabrasive layer 10 with thelaser beam 50 from the tangential direction, as shown in FIG. 13. A YAGlaser was employed for the laser beam. The output of the laser beam was40 W. The grooves were formed by applying the laser beam while rotatingthe dresser at a peripheral speed of 250 to 500 mm/min. The shape of thegrooves thus formed was as follows: They were screw-shaped grooves whosegroove pitch was 0.5 mm, the opening width of the grooves was 0.03 to0.08 mm, and the depth of the grooves was 0.03 mm.

In order to confirm the performance of the diamond rotary dressermanufactured in the aforementioned manner, a conventional grindstonemounted on a horizontal spindle surface grinding machine was dressedwith the diamond rotary dresser under the following conditions: As tothe grinding machine, a horizontal spindle surface grinding machine byOkamoto Machine Tool Works, Ltd. was employed. As to the driver for thediamond rotary dresser, the driver SGS-50 by Osaka Diamond IndustrialCo., Ltd. was employed. As to the shape of the dressed conventionalgrindstone, the outer diameter was 300 mm and the thickness was 10 mm,and its type was WA80K (type of JIS). As to the dressing conditions, theperipheral speed ratio was 0.28 (down-dressing), the cutting speed was1.9 mm/min., and the cutting amount was 4 mm.

The resistance value in the aforementioned dressing was compared withthat of an ungrooved conventional diamond rotary dresser. The dressingresistance value of the conventional diamond rotary dresser with nogrooves was 4.0N/10 mm in the normal direction and 0.5N/10 mm in thetangential direction. On the other hand, the dressing resistance valueof the diamond rotary dresser manufactured according to this Example was2.5N/10 mm in the normal direction and 0.25N/10 mm in the tangentialdirection.

Thus, the diamond rotary dresser of the present invention subjected togrooving by laser beam irradiation, showed a resistance value indressing reduced at least by 40 to 50% as compared with the conventionalproduct and was capable of smooth dressing without causing vibration.The accuracy of the dressed grindstone was also excellent.

EXAMPLE 5

A diamond rotary dresser was prepared as the straight-type abrasivedresser 103 shown in FIG. 5 and FIG. 6. The diameter D of the diamondrotary dresser was 80 mm, and the thickness T was 25 mm.

The grooves shown in FIG. 24 were formed on the exposed surface of thesuperabrasive layer. The grooves 12 were formed on the flat surface 19of each superabrasive grain 11 consisting of a diamond grain. Thesuperabrasive grain 11 was fixed to the base 20 through the brazingfiller metal layer 18 consisting of an Ag—Cu—Ti system alloy.

In Example 5, the grain sizes of the superabrasive grains 11, the shapeof the grooves 12 and the shape and the material of the base 20 aresimilar to Example 4. The distinguishing feature is that thesuperabrasive grains 11 were directly fixed to the base 20 with thebrazing filler metal layer 18.

This fixation was performed by applying a paste brazing filler metal toa surface of a base material 18, manually arranging the superabrasivegrains 11, thereafter introducing the same into a furnace, melting thebrazing filler metal by heating, and thereafter cooling the same.Therefore, while in example 4 the exposed surfaces of the superabrasivegrains 11 are substantially on the same plane as the surface of thenickel plating layer 16 (refer to FIG. 33), the exposed surfaces of thesuperabrasive grains 11 as shown in FIG. 24 project from the surface ofthe brazing filler metal layer 18 serving as the holding layer. Endsurfaces of the projecting superabrasive grains 11 were flattened bytruing, and grooves were formed on the flat surfaces by applying a laserbeam similarly to Example 4. In this case, it is also possible to omitthe truing.

This brazing type diamond rotary dresser has such excellentcharacteristics that elimination of chips in dressing is smoothlyperformed, and not only is dressing resistance low, but also there is nooccurrence of clogging since the amounts of projection of the diamondgrains are large as compared with the diamond rotary dresser of Example4 and abrasive grain spaces are extremely enlarged.

Further, because a forward end portion of a cutting edge of each diamondgrain of the superabrasive grain 11 is increased to a plurality ofcutting edges, i.e., the effective abrasive grain number is increaseddue to formation of the grooves 12 and consequently, sharpness andaccuracy also improve. Incidentally, in case of dressing employing thediamond rotary dresser manufactured in accordance with Example 5, it waspossible to reduce the required dressing time at least by about 30% ascompared with dressing by a conventional product.

The Ag—Cu—Ti system activated brazing filler metal employed as thebrazing filler metal in Example 5 is excellent in that the same canreadily strongly fix the diamond and the steel forming the base.However, the hardness of the brazing filler metal is at a low level ofabout Hv 100, and hence, there is the risk that the brazing filler metalsurface will be gradually eroded by contact of chips. Although this willcause no abrasion on the diamond grains in dressing, the brazing fillermetal will finally drop the diamond grains which will rapidly reduce thelife of the diamond rotary dresser.

Accordingly, an effective way of improving wear resistance of thebrazing filler metal is to introduce hard grains into the brazing fillermetal, in order to prevent the brazing filler metal from being eroded bythe chips. It is possible to prevent erosion of the brazing filler metalby introducing at least a single type of diamond, CBN, SiC abrasivegrains, Al₂O₃ abrasive grains, WC grains and the like into the brazingfiller metal as the hard grains. Grain sizes should not be more than ½that of the diamond grains employed for the rotary dresser. The ratio ofthese hard grains is within the range of 10 to 50 volume % with respectto the volume of the brazing filler metal, and preferably within therange of 30 to 50 volume %.

Example 4 is also executable by forming the nickel plating layer by theso-called inversion plating method similarly to Example 2 and providinggrooves on the nickel plating layer. Further, the superabrasive layeraccording to the present invention can be formed also by forming grooveson the layer formed as the holding layer by sintering metal powder oralloy powder known as metal bond. However, a dresser comprising a modeof fixing superabrasive grains with a brazing filler metal as shown inExample 5 can attain the highest dressing accuracy, and its dressingresistance is low. Further, a rotary dresser fixing superabrasive grainswith a brazing filler metal layer has long life, and it is possible toreduce its manufacturing time too.

EXAMPLE 6

A diamond rotary dresser was manufactured as the superabrasive dresser104 as shown in FIG. 7. Diamond grains of #50/60 in grain size (grainsize: 260 to 320 μm) were employed as the superabrasive grains. A nickelplating layer was employed as the holding layer, for holding thesuperabrasive grains in a single layer with the so-called inversionplating method as shown in Example 2, and bonding the same to the baseof steel.

Grooves were formed by performing truing on the surface of thesuperabrasive layer positioned on the shoulder portion 21 of the dresser104 in FIG. 7 to a thickness of 3 μm and thereafter applying the laserbeam while rotating the dresser at a peripheral speed of 250 to 500mm/min. As shown in FIG. 13, the laser beam 50 was applied to thesuperabrasive layer in the tangential direction. A YAG laser wasemployed for the laser beam. The output of the laser beam was 40 W. Asshown in FIG. 33, the grooves 12 were formed on the flat surface 19 ofeach superabrasive grain 11, and grooves 13 were formed on the surfaceof the nickel plating layer 16. They were screw-shaped grooves at agroove pitch of 0.3 mm, the opening width of the grooves was 0.03 to0.08 mm, and the depth of the grooves was 0.03 mm.

A microphotograph (magnification: 200) showing the arrangement of thegrooves formed in the shape of lines defining clearances on a go boardor checkerboard by laser beam irradiation was similar to that shown inFIG. 50.

In order to confirm the performance of the manufactured diamond rotarydresser, the dresser 104 was arranged as shown in FIG. 51 for dressing agrindstone 200. A workpiece 300 was ground with the WA (type of JIS)grindstone 200 of 300 mm in outer diameter, while the grindstone 200 wasdressed with the diamond rotary dresser 104 of 120 mm in outer diameter.The superabrasive layer 10 is formed on the outer peripheral surface ofthe base 20 of the diamond rotary dresser 104. The grooves are formed onthe shoulder portion 21 of the superabrasive layer 10 in theaforementioned manner. The outer peripheral shape of the grindstone 200is formed in correspondence to stepped portions 301 and 302 of theworkpiece 300. Arrows shown in FIG. 51 show rotational directions of theworkpiece 300, the grindstone 200 and the diamond rotary dresser 104respectively. The dressed conventional grindstone was WA80K in the typeof JIS. As to the dressing conditions, the peripheral speed ratio was0.3 (down-dressing), the cutting speed was 1.0 mm/min., and the cuttingamount was 4 mm.

The resistance value in dressing in Example 6 was compared with that ofan ungrooved conventional diamond rotary dresser. The dressingresistance value of the conventional diamond rotary dresser with nogrooves was 6.0N/10 mm in the normal direction, and 0.8N/10 mm in thetangential direction. On the other hand, the dressing resistance valueof the diamond rotary dresser of Example 6 was 4.0N/10 mm in the normaldirection, and 0.4N/10 mm in the tangential direction.

EXAMPLE 7

A diamond rotary dresser was manufactured as the superabrasive dresser105 having the outer peripheral shape shown in FIG. 8. Manufacturing ofthe dresser 105 and formation of grooves were performed similarly toExample 6. The grooves were formed by irradiating only the end surfaces22 and 23 of the dresser 105 shown in FIG. 8 with a laser beam from thetangential direction. A schematic section of the superabrasive layerformed with the grooves is as shown in FIG. 33.

In order to confirm the performance of the dresser manufactured in thismanner, a conventional grindstone was dressed with the dressermanufactured in Example 7 in conditions similar to Example 6.

As shown in FIG. 52, the diamond rotary dresser was arranged as asuperabrasive dresser 105 of 150 mm in diameter. A workpiece 300 wasground with a conventional grindstone 200 of WA or GC (type of JIS)having an outer diameter of 355 mm, while the grindstone 200 was dressedwith the diamond rotary dresser 105 of 150 mm in outer diameter. Thesuperabrasive layer 10 is formed on the outer peripheral surface of thebase 20 of the diamond rotary dresser 105. The grooves are formed onlyon the end surfaces 22 and 23 of the superabrasive layers 10 with alaser beam as described above.

The dressing resistance value of the diamond rotary dresser of Example 7was also reduced as compared with the dressing resistance value of aconventional diamond rotary dresser having no grooves, similarly toExample 6.

Thus, in the inventive diamond rotary dresser subjected to grooving bylaser beam irradiation, the resistance value in dressing was reduced byat least 30 to 50% as compared with the conventional product, novibration was caused, and smooth dressing was possible. Further,accuracy of the dressed grindstone was also excellent.

EXAMPLE 8

Diamond rotary dressers 104 and 105 of shapes similar to Examples 6 and7 were manufactured while changing the holding layers from the nickelplating layers to brazing filler metal layers.

A schematic section of a superabrasive layer formed with grooves is asshown in FIG. 24. The grooves 12 are formed on a flat surface 19 of eachsuperabrasive grain 11 consisting of a diamond grain. The superabrasivegrain 11 is held by a brazing filler metal layer 18 consisting of anAg—Cu—Ti alloy, and fixed to a base 20. The grain size of the diamondgrain, the shape of the grooves 12 and the shape and the material of thebase 20 are similar to Examples 6 and 7. A distinguishing feature isthat the diamond grain was directly fixed to the base 20 by the brazingfiller metal layer 18 as the superabrasive grain.

This fixation was performed by applying a paste brazing filler metal tothe base 20, manually placing the diamond grains, introducing the sameinto a furnace, melting the brazing filler metal by heating, andthereafter cooling the same. Therefore, while in Examples 6 and 7 asshown in FIG. 33 the exposed surface of each superabrasive grain 11 issubstantially on the same plane as the nickel plating layer 16 as theholding layer, in Example 8 as shown in FIG. 24 the exposed surface ofeach superabrasive grain 11 projects from the surface of the brazingfiller metal layer 18 serving as the holding layer. The grooves wereformed by flattening the projecting forward end portions by truing andirradiating the flat surfaces with a laser beam similarly to Examples 6and 7. The truing may be omitted as the case may be.

In the brazing type diamond rotary dresser manufactured in this manner,the amount of projection of the diamond grains is large as compared withExamples 6 and 7 as described above and an abrasive space is extremelyenlarged. Elimination of chips in dressing is smoothly performed, anddresser has such excellent characteristics that not only is the dressingresistance low, but there is no occurrence of clogging.

Due to formation of the grooves 12, further, the forward end portion ofa cutting edge of each superabrasive grain 11 is increased to aplurality of cutting edges, i.e., the effective abrasive grain number isincreased, whereby sharpness and accuracy improve.

The Ag—Cu—Ti activated brazing filler metal employed as the brazingfiller metal in Example 8 is excellent in that it can readily stronglyfix the diamond and the steel forming the base. However, the hardness ofthe brazing filler metal is at a low level of about Hv 100, and hencethere is risk that this brazing filler metal will be gradually erodedfrom its surface by contact of chips. Although this causes no abrasionon the diamond grains in dressing, it will finally cause the fillermetal to drop the diamond grains, which will rapidly reduce the life ofthe diamond rotary dresser.

Accordingly, an effective measure to prevent the brazing filler metalfrom being eroded by the chips is to introduce hard grains into thebrazing filler metal to improve wear resistance of the brazing fillermetal. It is possible to prevent erosion of the brazing filler metal byintroducing at least one type of hard grain such as diamond, CBN, SiC,Al₂O₃, WC and the like into the brazing filler metal. The grain sizes ofthese hard grains should not be more than ½ that of the diamond grainsemployed for formation of the abrasive surface. The ratio of these hardgrains should be within the range of 10 to 50 volume % with respect tothe volume of the brazing filler metal, and preferably within the rangeof 30 to 50 volume %.

The diamond rotary dresser of the present invention can be manufacturedby forming a nickel plating layer by the inversion plating method andforming grooves on a superabrasive layer similarly to Examples 6 and 7,or by sintering metal powder or alloy powder known as metal bond forforming a holding layer and forming grooves on a superabrasive layer.However, the brazing type diamond rotary dresser fixing thesuperabrasive grains with the brazing filler metal layer as describedabove has the highest dressing accuracy and its dressing resistance isalso low. Moreover, it is possible to reduce the manufacturing time ofthe dresser by selectively flattening only a prescribed portion in adressing operating surface, e.g., only a shoulder portion or an endsurface and selectively performing grooving. Further, a compositeddressing operating surface of a higher degree can be formed by changingthe grain sizes of the employed superabrasive grains, the degree ofconcentration and the like between this selected portion and theremaining portions.

As described above, the dresser of the present invention brings thestructure of the dressing operating surface into a specific structure,and hence it is necessary to bring the superabrasive grains into onelayer.

If the surface of the superabrasive layer is not a flat surface, a flatsurface is formed by truing and thereafter irradiated with a laser beam,and hence the grain sizes of the superabrasive grains may notnecessarily be uniformly regular.

If the grain sizes of the superabrasive grains are not substantiallyuniformly regular, however, the number of superabrasive grains on whichgrooves on flat surfaces cannot be formed increases and the prescribedfunction/effect may not be attained. When the grain sizes of thesuperabrasive grains are substantially uniformly regular, it is easy toperform truing, and prescribed grooves can be formed even if the amountof removal by truing is small, or without performing truing as the casemay be. Further, it is also possible to recycle the dresser byirradiating with a laser beam and forming grooves only on a prescribedportion of the superabrasive layer of the dresser whose sharpnessdecreases with use.

EXAMPLE 9

A diamond lap surface plate was manufactured as the superabrasive lapsurface plate 106 shown in FIG. 9 and FIG. 10. The diameter D of thediamond lap surface plate 106 was 300 mm, and the thickness T was 30 mm.A superabrasive layer was fixed onto the surface of the base 20 by onelayer.

As shown in FIG. 53, grooves 12 were formed on flat surfaces 19 ofsuperabrasive grains 11 consisting of diamond grains of #30/40 (grainsize: 430 to 650 μm) in grain size. The superabrasive grains 11 werefixed onto the base 20 by a brazing filler metal layer 18.

Fixation of the superabrasive grains 11 was performed by applying apaste brazing filler metal to the base 20, arranging diamond as thesuperabrasive grains in the brazing filler metal and introducing thebase 20 into a furnace, melting the brazing filler metal by heating andthereafter cooling the base 20. Therefore, projecting end surfaces ofthe superabrasive grains 11 projected beyond the surface of the brazingfiller metal layer 18 as a holding layer. The forward end portions ofthe projecting superabrasive grains 11 were flattened by truing, and theflat surfaces were irradiated with a laser beam for forming the grooves.

Formation of the grooves was performed by applying the laser beam 50 inthe normal direction with respect to the surface of the superabrasivelayer 10 as shown in FIG. 14. A YAG laser was employed for the laserbeam. The output of the laser beam was 2.5 W.

The grooves 12 arranged as shown in FIG. 39 were formed by applying thelaser beam in the form of meshes. Thus, the groove-to-groove pitch P was25 μm, t he width W of the grooves was 20 μm, the depth H of the grooveswas 20 μm, and the length W₀ of the flat parts between the grooves was 5μm, as shown in FIG. 53.

In the diamond lap surface plate manufactured in this manner, thediamond grains themselves scratch a workpiece, whereby high accuracylapping was enabled in high efficiency without supplying free abrasivegrains dissimilarly to a conventional lap surface plate of sphericalgraphite cast iron. Namely, the diamond lap surface plate of the presentinvention has such an excellent characteristic that sludge is hardlygenerated. This is because the sludge contains only a slight amount ofchips resulting from the workpiece when the workpiece is lapped. Thus,amount of sludge generated is extremely small. This enables not onlyworking in clean environment but also the amount of environmentalpollution generated is small.

Further, the diamond lap surface plate of the present invention isextremely excellent in wear resistance as compared with the conventionallap surface plate of spherical graphite cast iron. Furthermore, itshardness is uniform, and ability of the lap surface plate to maintainplane accuracy is also extremely high since its surface contains diamondgrains as superabrasive grains. Therefore, it can stably bring highplane accuracy and high parallel accuracy to a lapped workpiece over along period.

In addition, the diamond lap surface plate of the present invention hasabsolutely no defect corresponding to a cast defect which is regarded asthe largest problem in the lap surface plate of spherical graphite castiron. Therefore, no scratch results from a defect.

In order to confirm the performance of the diamond lap surface platemanufactured in Example 9, a comparative experiment with a conventionallap surface plate was performed. FIG. 54 shows results obtained bymounting this diamond lap surface plate on a lapping machine and lappinga silicon wafer.

The lapping shown in FIG. 54 was performed in the following workingconditions: The pressure was set at 200 g/cm², the rotational number wasset at 40 rev/min., the working fluid was prepared from water, theamount of supply of the working fluid was set at 10 cc/min., and theworkpiece was prepared from a silicon wafer of 50 mm in diameter.

Referring to FIG. 54, black triangles designating “lap surface plate 1”show measurement results achieved with the diamond lap surface plate ofExample 9 . According to these results, the working speed by the diamondlap surface plate of Example 9 was about three times the working speedby a conventional lap surface plate of spherical graphite cast ironemploying alumina of 5 μm in grain size as free abrasive grains.Further, surface roughness of the silicon wafer after lapping was alsoexcellent.

EXAMPLE 10

The diamond lap surface plate shown in FIG. 9 and FIG. 10 wasmanufactured similarly to Example 9. As to features different from thediamond lap surface plate of Example 9 , the groove-to-groove pitch Pwas 35 μm, and the length W₀ of the flat parts between the grooves was15 μm in FIG. 53. The remaining shape and dimensions of the diamond lapsurface plate, the forming method and the dimensions of the grooves andthe like were rendered similar to Example 9.

In order to confirm the performance of the diamond lap surface plate ofExample 10 , a silicon wafer was lapped in conditions similar to Example9 . Results thereof are shown in FIG. 54. Referring to FIG. 54, blacksquares designating “lap surface plate 2” show measurement resultsachieved with the diamond lap surface plate of Example 10.

As apparent from FIG. 54, the working speed by the diamond lap surfaceplate of Example 10 was about three times the working speed by aconventional lap surface plate of spherical graphite cast iron employingalumina of 12 μm in grain size as free abrasive grains. Further, surfaceroughness of the silicon wafer after lapping was also excellent.

EXAMPLE 11

The cup-type superabrasive grindstone 101 as shown in FIG. 1 and FIG. 2was manufactured. The diameter D of the grindstone was 125 mm, and thewidth W₁ of the abrasive surface was 7 mm. Diamond grains of #18/20(mean grain size: 900 μm) in grain size were employed as thesuperabrasive grains. The superabrasive grains were fixed to the surfaceof the base 20 by a nickel plating layer.

Flat surfaces were formed by removing forward end portions of thesuperabrasive grains with a diamond grindstone of #120 in grain size bya thickness of 30 μm. Thereafter a laser beam was intermittently appliedwith respect to the surface of the superabrasive layer 10 in the normaldirection as shown in FIG. 11, thereby forming holes on the flatsurfaces of the superabrasive grains. A YAG laser was employed for thelaser beam. The output of the laser beam was 2.5 W.

A section of the superabrasive layer including holes thus formed is asshown in FIG. 27. The dimensions of the holes are shown in FIG. 55. Thediameter D₁ of the holes was 50 μm, the depth H₁ of the holes was 30 to50 μm, and the space between the holes 14 was 100 μm. Namely, the holes14 were formed on intersections in the form of lines defining clearanceson a go board or checkerboard at the pitch of 100 μm.

Grinding performance was confirmed by employing the cup-typesuperabrasive grindstone manufactured in the aforementioned manner. Avertical spindle surface grinding machine was employed as a grindingmachine, and a silicon single crystal was employed as a workpiece. Whenemploying the cup-type superabrasive grindstone of the present inventionformed with the holes, grinding resistance was reduced by 20 to 30% ascompared with a cup-type superabrasive grindstone having no holes.

EXAMPLE 12

A diamond rotary dresser was manufactured as the superabrasive dresser103 shown in FIG. 5 and FIG. 6. The diameter D of the dresser was 80 mm,and the thickness T was 20 mm. Diamond grains of #50/60 (mean grainsize: 300 μm) in grain size were employed as the superabrasive grains. Afixation method of the superabrasive grains to the base 20 was performedby the so-called inversion plating method shown in Example 2.

Holes were formed on flat surfaces of the superabrasive grains byintermittently applying a laser beam with respect to the superabrasivelayer 10 in the vertical direction as shown in FIG. 12. A YAG laser wasemployed for the laser beam. The output of the laser beam was 2.5 W.

The superabrasive layer 10 having the holes 14 as shown in FIG. 27 wasformed in this manner. The diameter D₁ of the holes was 50 μm, the depthH₁ of the holes was 30 to 50 μm, and the pitch between the holes 14 was100 μm, as shown in FIG. 55.

The performance was confirmed by employing the diamond rotary dressermanufactured in the aforementioned manner. A horizontal spindle surfacegrinding machine was employed as a grinding machine. As to the driverfor the diamond rotary dresser, one by Osaka Diamond Industrial Co.,Ltd. (type SGS-50 type) was employed. WA80K (JIS type) was employed asthe grindstone of the dressed object, the diameter of the grindstone was300 mm, and the width was 15 mm. As to dressing conditions, theperipheral speed ratio was 0.3, and the cutting speed was 2 mm/min.

According to the rotary dresser of the present invention comprisingholes, the dressing resistance value was reduced by 20 to 30% ascompared with the conventional rotary dresser.

In the stages of fixing the superabrasive grains to the bases andforming the superabrasive layers in the aforementioned Examples 11 and12, truing for substantially uniformly regularizing the heights of theprojecting parts of the superabrasive grains was performed andthereafter application of laser beams was intermittently performed atthe pitches of 100 μm, for forming holes on the flat surfaces of thesuperabrasive grains while changing the positions. Single or pluralholes were formed on the forward end portions of the exposedsuperabrasive grains in Examples 11 and 12. However, holes can be formedto extend over the boundaries between the exposed portions of thesuperabrasive grains and the exposed portion of the nickel plating layerserving as the holding layer forming the superabrasive layer and on theexposed portion of the holding layer in application of the laser beam. Asuperabrasive tool which is further excellent in performance can beobtained by thus forming the holes on the overall surface of thesuperabrasive layer.

FIG. 56 is a microphotograph (magnification: 50) showing the arrangementof holes formed on a superabrasive layer according to an Exampledifferent from the aforementioned Examples. Referring to FIG. 56, thearea in a black frame appearing in the form of a peninsula from theupper portion is a superabrasive grain, and the small individual,scatteredly appearing black areas in the superabrasive grain are holes.The holes are formed also on the surface of the nickel plating layer.Therefore, the holes 14 may be formed only on the flat surface 19 of thesuperabrasive grain 11 as in FIG. 27, or the holes 14 may be formed onthe flat surface 19 of the superabrasive grain 11 and the holes 15 maybe also formed on the surface of the nickel plating layer 16 as shown inFIG. 29.

Recycling of a tool is also enabled by forming holes in a superabrasivelayer of a superabrasive tool whose sharpness reduces by use, byirradiating the same with a laser beam.

EXAMPLE 13

The diamond rotary dressers 103 shown in FIG. 5 and FIG. 6 weremanufactured. The diameter D of the dressers was 100 mm, and thethickness T was 15 mm. Dressers employing respective ones of two typesof diamond grains of #30/40 (grain size 400 to 600 μm) in grain size and#50/60 (grain size 250 to 320 μm) in grain size as the superabrasivegrains were manufactured. Nickel plating layers were employed as theholding layers. The superabrasive grains were fixed onto bases so thatexposed surfaces of the superabrasive grains projected from surfaces ofthe nickel plating layers, and thereafter truing was performed on theforward end portions of the superabrasive grains with a diamondgrindstone of #120 in grain size. Thereafter the laser beam 50 wasapplied with respect to the superabrasive layers from the tangentialdirection as shown in FIG. 13 while rotating the dressers at aperipheral speed of 250 to 500 mm/min., thereby forming screw-shapedgrooves. Two types of respective dressers were manufactured asgroove-to-groove pitches of 0.3 mm and 0.5 mm. The depth of the grooveswas 20 μm, and the width of the grooves was 20 μm.

Conventional grindstones were dressed with four types of diamond rotarydressers manufactured by rendering the grain sizes of the tionalgrindstones, and the cutting amount was set at 0.02 mm. Further,dressing-out was set at 1 sec.

Measurement results of dressing resistance values are shown in Table 1.

TABLE 1 Change of Dressing Resistance (unit: KW) Diamond Grain SizeDiamond Grain Size #30/40 #50/60 Pitch 0.5 Pitch 0.3 Pitch 0.5 Pitch 0.3Before Laser 0.30 0.30 0.30 0.30 Grooving After Laser 0.28 0.20 0.280.17 Grooving Amount of 0.02 0.10 0.02 0.13 Change

As seen in Table 1, the dressing resistance values decrease when thediamond rotary dressers subjected to grooving are employed. It can beseen that the ratio of reduction of the dressing resistance valueincreases when the groove-to-groove pitch in particular is reduced. Itcan also be seen that the reduction ratios of the dressing resistancevalues increase with reduced grain sizes of the diamond grains.

As hereinabove described, the superabrasive tool according to thepresent invention is useful as a grindstone employing superabrasivegrains of diamond, cubic boron nitride (CBN) or the like, asuperabrasive dresser utilized for dressing a conventional grindstone orthe like mounted on a grinding machine or the like, or a superabrasivelap surface plate employed for lapping of a silicon wafer or the like,and suitable for performing working resistance value increases when thegroove-to-groove pitch in particular is reduced. It can also be seenthat the reduction ratios of the dressing resistance values increasewith reduced grain sizes of the diamond grains.

As hereinabove described, the superabrasive tool according to thepresent invention is useful as a grindstone employing superabrasivegrains of diamond, cubic boron nitride (CBN) or the like, asuperabrasive dresser utilized for dressing a conventional grindstone orthe like mounted on a grinding machine or the like, or a superabrasivelap surface plate employed for lapping of a silicon wafer or the like,and suitable for performing working of high accuracy in particular.

What is claimed is:
 1. A superabrasive tool comprising: a base (20); anda superabrasive layer (10) formed on said base (20); wherein saidsuperabrasive layer (10) includes a holding layer (16, 17; 18) thataffixes said superabrasive layer (10) to said base (20), andsuperabrasive grains (11) that are partially embedded and held in saidholding layer and that are discretely dispersed and spaced apart fromeach other so as to form an arrangement of dispersed ones of saidsuperabrasive grains (11) having exposed grain surfaces and of exposedholding layer surface areas of said holding layer exposed between saidsuperabrasive grains, and wherein said exposed grain surfaces have firstconcavities therein.
 2. The superabrasive tool in accordance with claim1, wherein said first concavities are grooves (12).
 3. The superabrasivetool in accordance with claim 1, wherein said first concavities areholes (14).
 4. The superabrasive tool in accordance with claim 1,wherein said exposed holding layer surface areas of said holding layer(16, 17; 18) have second concavities (13; 15) therein.
 5. Thesuperabrasive tool in accordance with claim 4, wherein said firstconcavities (12; 14) in said exposed grain surfaces of saidsuperabrasive grains and said second concavities (13; 15) in saidexposed holding layer surface areas of said holding layer (16, 17; 18)are continuous with each other from said exposed grain surfaces to saidexposed holding layer surface areas.
 6. The superabrasive tool inaccordance with claim 1, wherein said exposed grain surfaces of saidsuperabrasive grains (11) project and protrude from said holding layer(16, 17; 18).
 7. The superabrasive tool in accordance with claim 6,wherein said exposed grain surfaces of said superabrasive grains (11)are flat planar surfaces (19), and said first concavities (12, 14) areformed on said flat planar surfaces (19).
 8. The superabrasive tool inaccordance with claim 1, wherein said exposed grain surfaces of saidsuperabrasive grains (11) are flat planar surfaces (19) that aresubstantially parallel to said exposed holding layer surface areasdefining a surface of said holding layer (16, 17; 18).
 9. Thesuperabrasive tool in accordance with claim 8, wherein said exposedholding layer surface areas of said holding layer (16, 17; 18) havesecond concavities (13; 15) therein.
 10. The superabrasive tool inaccordance with claim 9, wherein said first concavities (12; 14) in saidexposed grain surfaces of said superabrasive grains and said secondconcavities (13; 15) in said exposed holding layer surface areas of saidholding layer (16, 17; 18) are continuous with each other from saidexposed grain surfaces to said exposed holding layer surface areas. 11.The superabrasive tool in accordance with claim 1, wherein said holdinglayer includes a plating layer (16).
 12. The superabrasive tool inaccordance with claim 1, wherein said holding layer includes a brazingfiller metal layer (18).
 13. The superabrasive tool in accordance withclaim 1, wherein said superabrasive tool is a superabrasive grindstone(101; 102).
 14. The superabrasive tool in accordance with claim 1,wherein said superabrasive tool is a superabrasive dresser (103; 104;105).
 15. The superabrasive tool in accordance with claim 1, whereinsaid superabrasive tool is a superabrasive lap surface plate (106). 16.A method of manufacturing a superabrasive tool according to claim 1,comprising the steps of: forming said holding layer (16, 17; 18) holdingand fixing said superabrasive grains (11) on said base (20) so thatsurfaces of said grains are partially exposed from said holding layer toprovide said exposed grain surfaces; and forming said first concavities(12; 14) by irradiating said exposed grain surfaces with a laser beam(150).
 17. The method of manufacturing a superabrasive tool inaccordance with claim 16, further comprising a step of forming secondconcavities by irradiating said exposed holding layer surface areas witha laser beam (50).
 18. The method of manufacturing a superabrasive toolin accordance with claim 17, wherein said steps of forming said firstconcavities on said exposed grain surfaces and forming said secondconcavities on said exposed holding layer surface areas includeoperations of forming said first and second concavities respectively(12;14, 13; 15) on said exposed grain surfaces and on said exposedholding layer surface areas by continuously irradiating said exposedgrain surfaces and said exposed holding layer surface areas with saidlaser beam (50).
 19. The method of manufacturing a superabrasive tool inaccordance with claim 16, wherein said step of forming said firstconcavities (12; 14) includes an operation of forming first concavities(12; 14) by irradiating with said laser beam (50) said exposed grainsurfaces of said superabrasive grains (11) that project from saidholding layer (16, 17; 18).
 20. The method of manufacturing asuperabrasive tool in accordance with claim 16, further comprising astep of substantially uniformly flattening said exposed grain surfacesof said superabrasive grains (11) to form uniformly flat surfaces (19)of said grains exposed from said holding layer (16, 17; 18), and whereinsaid step of forming said first concavities (12; 14) includesirradiating said uniformly flat surfaces (19) with said laser beam (50).21. The method of manufacturing a superabrasive tool in accordance withclaim 20, wherein said step of flattening said exposed grain surfaces iscarried out so that said exposed grain surfaces form a planesubstantially parallel to a surface of said holding layer (16, 17; 18)defined by said exposed holding layer surface areas.
 22. The method ofmanufacturing a superabrasive tool in accordance with claim 21, furthercomprising a step of forming second concavities (13; 15) by irradiatingsaid exposed holding layer surface areas of said holding layer (16, 17;18) with a laser beam, wherein said steps of forming said first andsecond concavities respectively (12; 14, 13; 15) on said exposed grainsurfaces and on said exposed holding layer surface areas includeoperations of continuously forming said first and second concavities(12; 14, 13; 15) on said uniformly flat surfaces (19) of said exposedgrain surfaces and on said exposed holding layer surface areas bycontinuously irradiating said exposed grain surfaces and said exposedholding layer surface areas with said laser beam (50).
 23. The method ofmanufacturing a superabrasive tool in accordance with claim 16, whereinsaid step of forming said holding layer includes an operation of forminga plating layer (16).
 24. The method of manufacturing a superabrasivetool in accordance with claim 23, wherein said step of forming saidholding layer includes the steps of: sticking said superabrasive grains(11) to a surface of a mold (60) with a conductive adhesive layer (70),forming a first plating layer (80) of a first metal that partiallycovers said exposed grain surfaces of said superabrasive grains (11) ina first plating layer thickness of less than ½ a mean grain size of saidsuperabrasive grains (11) by dipping said mold (60) to which saidsuperabrasive grains (11) are stuck in a plating solution of said firstmetal, forming a second plating layer (16) of a second metal beingdifferent from said first metal with a second plating layer thicknessthat completely covers holding surfaces of said superabrasive grains(11) on said first plating layer (80) of said first metal, fixing saidsecond plating layer (16) of said second metal to said base (20) by abond layer (17), removing said mold (60) from said superabrasive grains(11), and removing said first plating layer (80) of said first metal byetching and partially uniformly exposing said exposed grain surfaces ofsaid superabrasive grains (11).
 25. The method of manufacturing asuperabrasive tool in accordance with claim 16, wherein said step offorming said holding layer includes an operation of forming a brazingfiller metal layer (18).